My DS is 10. His DF left in 2013. When he left, he contacted the CSA and told me he would voluntarily pay me £350 per month. I have no idea what he earned. He did say that he had rounded it up to make it a better number. By how much, I don't know. FF to 2021 and I am struggling financially. My hours have been cut drastically and my DS has outgrown all his clothes and I have our mortgage to pay. I asked if ExH would just consider an increase in his maintenance. He said he couldn't afford to, he's struggling financially because of Covid (he's a keyworker so no change in wages and he has no mortgage or rent). He says he has been in contact with the CMS and he has been overpaying me, I'm entitled to £210 per month. The CMS have said he can claim back all the money he has over paid.
YABU - of course I should pay it back, I wasn't entitled to it.
YANBU - he knowingly and voluntarily overpaid so I should not have to pay to back.